Lusters are the elves' currency. One luster is equivalent to about 1 million human dollars. At birth, every elf is given a birth fund of 5 million lusters, making each birth fund worth about $5,000,000,000,000. Lusters are stored in a green cube called a Treasury Cube carried by each elf. In order to pay lusters to another elf, one would swipe the green cube against a machine called a Deducter.
Although most elves obtain their funds at birth, Sophie Foster received hers when she first arrived at the Lost Cities in Keeper of the Lost Cities since she was born in the Forbidden Cities to a human family.